<meta charset="utf-8">
(#) Notification Trampolines

!!! ERROR: Notification Trampolines
   This is an error.

Id
:   `NotificationTrampoline`
Summary
:   Notification Trampolines
Severity
:   Error
Category
:   Performance
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   4.3.0-alpha01 (December 2020)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/NotificationTrampolineDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NotificationTrampolineDetectorTest.kt)

Activities should not be launched indirectly from a notification via an
intermediate `BroadcastReceiver` or `Service`. This can lead to
significant lags in some scenarios, and is forbidden if
`targetSdkVersion` is set to the API level for Android 12 or higher.

To fix this, launch the `Activity` directly from the notification.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/NotificationTest.java:36:Error: This intent launches a
BroadcastReceiver (BroadcastTrampoline) which launches activities; this
indirection is bad for performance, and activities should be launched
directly from the notification [NotificationTrampoline]
    .setContentIntent(notificationPendingIntent)
     -------------------------------------------
src/test/pkg/NotificationTest.java:38:Error: This intent launches a
BroadcastReceiver (BroadcastTrampoline) which launches activities; this
indirection is bad for performance, and activities should be launched
directly from the notification [NotificationTrampoline]
    .addAction(android.R.drawable.ic_dialog_email, "Launch Receiver From Action",
     ^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/test/pkg/BroadcastTrampoline.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class BroadcastTrampoline extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // The start below will be blocked
        Intent i = new Intent();
        i.setClassName("test.pkg", "test.pkg.SecondActivity");
        i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        context.startActivity(i);
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/NotificationTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Build;

import androidx.core.app.NotificationCompat;

import static android.app.Notification.EXTRA_NOTIFICATION_ID;

public class NotificationTest {
    public static final String ACTION_LAUNCH =
            "test.pkg.action.LAUNCH";

    public void test(Context context, String channelId, int id, int requestCode, int flags) {
        Intent notificationIntent = new Intent(context, test.pkg.BroadcastTrampoline.class);
        PendingIntent notificationPendingIntent = PendingIntent.getBroadcast(context, requestCode, notificationIntent, flags);

        Intent broadcastIntent = new Intent(context, BroadcastTrampoline.class);
        broadcastIntent.setAction(ACTION_LAUNCH);
        broadcastIntent.putExtra(EXTRA_NOTIFICATION_ID, id);
        notificationIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);

        PendingIntent broadcastPendingIntent =
                PendingIntent.getBroadcast(context, 0, broadcastIntent, 0);

        NotificationCompat.Builder builder =
                new NotificationCompat.Builder(context, channelId)
                        .setSmallIcon(android.R.drawable.ic_menu_my_calendar)
                        .setContentTitle("Notification Trampoline Test")
                        .setContentText("Tap this notification to launch a new receiver")
                        .setPriority(NotificationCompat.PRIORITY_DEFAULT)
                        .setContentIntent(notificationPendingIntent)
                        .setAutoCancel(true)
                        .addAction(android.R.drawable.ic_dialog_email, "Launch Receiver From Action",
                                broadcastPendingIntent);
        Notification notification = builder.build();
        NotificationManager notificationManager =
                context.getSystemService(NotificationManager.class);
        notificationManager.notify(id, notification);
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/NotificationTrampolineDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `NotificationTrampolineDetector.testBroadcastTrampolineJava`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("NotificationTrampoline")
  fun method() {
     setContentIntent(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("NotificationTrampoline")
  void method() {
     setContentIntent(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection NotificationTrampoline
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="NotificationTrampoline" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'NotificationTrampoline'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore NotificationTrampoline ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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